拟南芥R2R3-MYB类转录因子在环境胁迫中的作用

MYB转录因子是植物转录因子中最大的家族之一,以含有保守的MYB结构域为共同特征,分为三个亚族（R1／2-MYB、R2R3-MYB和R1R2R3-MYB）,其中含有两个MYB结构域的R2R3-MYB成员最多,广泛参与植物次生代谢调控、细胞形态发生、胁迫应答、分生组织形成及细胞周期控制等。近年来,R2R3-MYB在植物逆境胁迫中的作用引起了广泛关注,本文综述了拟南芥R2R3-MYB蛋白在环境胁迫响应中作用的研究进展。     

The pleiotropic mutation dar1 affects plant architecture in Arabidopsis thaliana

Shoot architecture is shaped upon the organogenic activity of the shoot apical meristem (SAM). Such an activity relies on the balance between the maintenance of a population of undifferentiated cells in the centre of the SAM and the recruitment of organ founder cells at the periphery. A novel mutation in Arabidopsis thaliana, distorted architecture1 (dar1), is characterised by disturbed phyllotaxy of the inflorescence and consumption of the apical meristem late in development. SEM and light microscopy analyses of the dar1 SAM reveal an abnormal partitioning of meristematic domains, and mutations known to affect the SAM structure and function were found to interact with dar1. Moreover, the mutant shows an alteration of the root apical meristem (RAM) structure. Those observations support the hypothesis that DAR1 has a role in meristem maintenance and it is required for the normal development of Arabidopsis inflorescence during plant life.     

Establishment of a gene tagging system in Arabidopsis thaliana based on the maize transposable element Ac

Summary An Ac-derived, two-component transposable element system has been developed and analyzed with respect to its use in Arabidopsis thaliana. This system consists of an immobilized Ac element (Ac clipped wing, Ac_cl) as the source of transactivating transposase and a nonautonomous Ds element, Ds_A, which is inserted into a chimaeric neomycinphosphotransferase gene used as excision marker. After separate introduction of Ac_c1 and Ds_A into Arabidopsis thaliana, progeny analysis of crosses between five different Ac_cl lines and seven different Ds_A lines shows that: (1) different Ac_cl lines differ greatly in their capacity to transactivate Ds_A; (2) different Ds_A lines do not differ significantly with respect to Ds_A transactivation by one Ac_cl line; (3) reintegration of excised Ds_A elements, both at (genetically) linked and unlinked sites, occurs in about 50% of the excision events; and (4) plants with a high rate of somatic excisions can be used as source of new Ds_A transpositions, allowing the creation of a large number of independent Ds_A insertions.     

The isolation and characterisation of the tapetum-specific Arabidopsis thaliana A9 gene

The Brassica napus cDNA clone A9 and the corresponding Arabidopsis thaliana gene have been sequenced. The B. napus cDNA and the A. thaliana gene encode proteins that are 73% identical and are predicted to be 10.3 kDa and 11.6 kDa in size respectively. Fusions of an RNase gene and the reporter gene -glucuronidase to the A. thaliana A9 promoter demonstrated that in tobacco the A9 promoter is active solely in tapetal cells. Promoter activity is first detectable in anthers prior to sporogenous cell meiosis and ceases during microspore premitotic interphase.The deduced A9 protein sequence has a pattern of cysteine residues that is present in a superfamily of seed plant proteins which contains seed storage proteins and several protease and -amylase inhibitors.     

Adventitious root formation in Arabidopsis thaliana thin cell layers

This paper describes, for the first time, de novo adventitious root formation from thin cell layers (TCLs) of Arabidopsis thaliana. The objective of the study was to determine the optimal hormonal and light conditions and the optimal exogenous Ca²⁺ concentration for obtaining adventitious rooting (AR) from A. thaliana TCLs and to identify the tissue(s) involved in the process. The results show that maximum AR was obtained with a single-phase method in the presence of 10 M indole-3-butyric acid and 0.1 M kinetin under continuous darkness for 30 days and with 0.6 mM exogenous CaCl₂. The endodermis was the only tissue involved in root meristemoid formation. The role of Ca²⁺ in AR and the importance of using Arabidopsis TCLs in studies on the genetic/biochemical control of AR are discussed.Abbreviations AR Adventitious rooting - CIM Callus-inducing medium - Col-0 Columbia ecotype - 2,4-D 2,4-Dichlorophenoxyacetic acid - HFM Hormone-free medium - HM Medium with 10 M IBA and 0.1 M Kin - IBA Indole-3-butyric acid - Kin Kinetin - LS Longitudinal section - NAA -Naphthaleneacetic acid - RIM Root-inducing medium - TCL Thin cell layer - WS Wassilewskija ecotype     

Characterization of microstructure and cell wall components of Arabidopsis thaliana overexpressing cyclin-dependent kinase inhibitor 2

Overexpression of a cyclin-dependent kinase inhibitor (KRP2) caused changes in the general morphology in the leaves of Arabidopsis thaliana. The wild type plant had obovate leaves with entire margins whereas the transgenic line had leaves with denticulate margins. The epidermal cells and stomata of the adult transgenic leaves were significantly larger than those of the wild-type plants and the number of stomata was in proportion to the number of epidermal cells. No apparent differences in thickness and structure of cell walls of the mesophyll cells between the two samples were observed. The smaller amount of cell wall material in the transgenic leaves caused by the larger cell size was also apparent in the lower dry weight of the transgenic leaves. The chemical analysis revealed the main differences to be in pectin and neutral sugar contents, and especially in the amounts of glucose, all being higher in the leaves of the KRP2 transgenic plants. p-Coumaric acid content varied more in the transgenic leaf material than in the control one reflecting possibly fewer cross-links in the cell walls of transgenic plants.     

An in silico assessment of gene function and organization of the phenylpropanoid pathway metabolic networks in Arabidopsis thaliana and limitations thereof

The Arabidopsis genome sequencing in 2000 gave to science the first blueprint of a vascular plant. Its successful completion also prompted the US National Science Foundation to launch the Arabidopsis 2010 initiative, the goal of which is to identify the function of each gene by 2010. In this study, an exhaustive analysis of The Institute for Genomic Research (TIGR) and The Arabidopsis Information Resource (TAIR) databases, together with all currently compiled EST sequence data, was carried out in order to determine to what extent the various metabolic networks from phenylalanine ammonia lyase (PAL) to the monolignols were organized and/or could be predicted. In these databases, there are some 65 genes which have been annotated as encoding putative enzymatic steps in monolignol biosynthesis, although many of them have only very low homology to monolignol pathway genes of known function in other plant systems. Our detailed analysis revealed that presently only 13 genes (two PALs, a cinnamate-4-hydroxylase, a p-coumarate-3-hydroxylase, a ferulate-5-hydroxylase, three 4-coumarate-CoA ligases, a cinnamic acid O-methyl transferase, two cinnamoyl-CoA reductases) and two cinnamyl alcohol dehydrogenases can be classified as having a bona fide (definitive) function; the remaining 52 genes currently have undetermined physiological roles. The EST database entries for this particular set of genes also provided little new insight into how the monolignol pathway was organized in the different tissues and organs, this being perhaps a consequence of both limitations in how tissue samples were collected and in the incomplete nature of the EST collections. This analysis thus underscores the fact that even with genomic sequencing, presumed to provide the entire suite of putative genes in the monolignol-forming pathway, a very large effort needs to be conducted to establish actual catalytic roles (including enzyme versatility), as well as the physiological function(s) for each member of the (multi)gene families present and the metabolic networks that are operative. Additionally, one key to identifying physiological functions for many of these (and other) unknown genes, and their corresponding metabolic networks, awaits the development of technologies to comprehensively study molecular processes at the single cell level in particular tissues and organs, in order to establish the actual metabolic context.     

The structure of the major anthocyanin in Arabidopsis thaliana

The major anthocyanin in the leaves and stems of Arabidopsis thaliana has been isolated and shown to be cyanidin 3-O-[2-O(2-O-(sinapoyl)-beta-D-xylopyranosyl)-6-O-(4-O-(beta-D-glucopyranosyl)-p-coumaroyl-beta-D-glucopyranoside] 5-O-[6-O-(malonyl) beta-D-glucopyranoside]. This anthocyanin is a glucosylated version of one of the anthocyanins found in the flowers of the closely related Matthiola incana.     

Natural variation for seed oil composition in Arabidopsis thaliana

The biochemical pathways involved in the biosynthesis and accumulation of storage lipids in seeds have been extensively studied. However, the regulatory mechanisms of those pathways, their environmental interactions and the ecological implications of variation are poorly understood. We have initiated a new approach: the analysis of natural variation in Arabidopsis thaliana. Three hundred and sixty accessions were surveyed for content of oil, very long chain fatty acids (VLCFAs) and polyunsaturated fatty acids (PUFAs) in their seeds. The results revealed extensive natural variation. A core set of accessions, the seeds of which reproducibly contain extreme amounts of oil, VLCFAs and PUFAs have been identified. Reproducible oil content ranged from 34.6 to 46.0% of seed dry weight. VLCFA content ranged from 13.0 to 21.2% of total fatty acids. PUFA content, ranged from 53.3 to 66.1% of total fatty acids. Interactions were also identified for PUFA and VLCFA content of seeds with vernalisation of plants. Mapping of the regions of the genome involved in controlling the traits was conducted in an F(2) population and indicated that natural variation at the loci FAE1 and FAD3 might be involved in the regulation of VLCFA and PUFA content, respectively. A set of accessions, which capture a broad range of the natural variation for these traits available in A. thaliana, has been selected to form a core set which can be used to further dissect the genetics of the regulation of seed lipid traits and to identify the genes involved.     

Indole-3-butyric acid in Arabidopsis thaliana

Indole-3-butyric acid (IBA) was identified by HPLC and GC-MS as an endogenous compound in plantlets of the crucifer Arabidopsis thaliana (L.) Heynh. A. thaliana was cultivated under sterile conditions as shaking culture in different liquid media with and without supply of hormones. Free and total IBA and indole-3-acetic acid (IAA) were determined at different stages of development during the culture period as well as in culture media of different initial pH values. The results showed that IAA was present in higher concentrations than IBA, but both hormones seemed to show the same behaviour under the different experimental conditions. Differences were found in the mode of conjugation of the two hormones. While IAA was mostly conjugated via amide bonds, the main IBA conjugates were ester bound. The ethylene concentration derived from the seedlings, when they were grown in flasks of different size, seemed not to influence the auxin content in the same cultures.     

Embryo sac development in Arabidopsis thaliana II. The cytoskeleton during megagametogenesis

The microtubular and actin cytoskeletons have been investigated during megagametogenesis in Arabidopsis thaliana using immunofluorescence labelling of isolated coenocytic and mature embryo sacs. We found both actin and microtubules (MTs) to occur in abundance throughout megagametogenesis and in all constituent cells of the mature embryo sac. During many stages, the patterns of distribution of these cytoskeletal elements are congruent and may prove to be co-aligned. Many changes in the arrays of MTs and microfilaments take place and indicate varying roles of the cytoskeleton in the different stages and cell types of megagametogenesis. Two major populations of MTs recur throughout embryo sac formation: (1) Elaborate nuclear-based networks are found during the two-nucleate and four-nucleate developmental stages as well as in the egg cell. These arrays may function in positioning the nuclei. (2) Cytoplasmic MTs in longitudinal orientation in the two-nucleate embryo sac, synergids and part of the egg cell, or in a reticulate pattern in the four-nucleate embryo sac, egg and central cell probably participate in organization of the cytoplasm. Synergid MTs converge at the filiform apparatus. Preprophase bands of MTs are absent throughout megagametogenesis but phragmoplast arrays occur during cellularization of the embryo sac. Well developed arrays of cortical MTs are restricted to the antipodal cells. A large concentration of MTs in the part of the egg cell adjacent to the synergids is well placed for being involved with sperm cell movement within the degenerative synergid. On the basis of the morphology of the cytoskeleton, we concur with views that the shape of megagametophyte is largely determined by the surrounding tissues, including the integumentary tapetum.     

Developmental anatomy of cotyledons and leaves in has mutant of Arabidopsis thaliana

Summary. In this work, we analyzed the developmental anatomy of cotyledons and leaves in the has mutant of Arabidopsis thaliana. It is a recessive T-DNA insertion mutation that causes changes in the size, shape, and tissue organization of the cotyledons and leaves of has plants. Analysis of has cotyledons revealed a prominent decrease in the cell number and an increase in the area of cotyledon cells and intercellular spaces of has plants. At early stages of development, has leaves are fingerlike structures, but later they develop small, lobed blades with rare trichomes. An important characteristic of the mutant leaf anatomy is the absence of mesophyll tissue differentiation. In addition, both cotyledons and leaves display a disrupted pattern of vascular bundles. Furthermore, mutant plants are defective in root and shoot morphology, indicating that the has mutation affects a number of aspects in plant development. Correspondence and reprints: Institute of Botany and “Jevremovac” Botanical Garden, Faculty of Biology, Belgrade University, Takovska 43, 11 000 Belgrade, Serbia.     

Jasmonate biosynthesis and the allene oxide cyclase family of Arabidopsis thaliana

In biosynthesis of octadecanoids and jasmonate (JA), the naturally occurring enantiomer is established in a step catalysed by the gene cloned recently from tomato as a single-copy gene (Ziegler et al., 2000). Based on sequence homology, four full-length cDNAs were isolated from Arabidopsis thaliana ecotype Columbia coding for proteins with AOC activity. The expression of AOCgenes was transiently and differentially up-regulated upon wounding both locally and systemically and was induced by JA treatment. In contrast, AOC protein appeared at constitutively high basal levels and was slightly increased by the treatments. Immunohistochemical analyses revealed abundant occurrence of AOC protein as well as of the preceding enzymes in octadecanoid biosynthesis, lipoxygenase (LOX) and allene oxide synthase (AOS), in fully developed tissues, but much less so in 7-day old leaf tissues. Metabolic profiling data of free and esterified polyunsaturated fatty acids and lipid peroxidation products including JA and octadecanoids in wild-type leaves and the jasmonate-deficient mutant OPDA reductase 3 (opr3) revealed preferential activity of the AOS branch within the LOX pathway. 13-LOX products occurred predominantly as esterified derivatives, and all 13-hydroperoxy derivatives were below the detection limits. There was a constitutive high level of free 12-oxo-phytodienoic acid (OPDA) in untreated wild-type and opr3 leaves, but an undetectable expression of AOC. Upon wounding opr3 leaves exhibited only low expression of AOC, wounded wild-type leaves, however, accumulated JA and AOC mRNA. These and further data suggest regulation of JA biosynthesis by OPDA compartmentalization and a positive feedback by JA during leaf development.     

The Correlation between the Chromosome Variation in Callus and Genotype of Explants of Arabidopsis thaliana

Twelve callus lines of Arabidopsis thaliana were derived from four types of explants excised from diploid plants of two ecotypes (Columbia and Wilna) and autotetraploid plants of the Wilna ecotype. Cytogenetic analysis of the chromosome variation in particular callus lines was carried out for primary culture and callus during 5 months of culture. Ploidy levels of interphase nuclei were estimated by counting the number and size of chromocentres and nuclei of interphase cells. The first polyploid cells in all callus lines were observed during callogenesis. In primary culture the ploidy level ranged between 2 and 15x (10-75 chromosomes). The frequency of polyploid cells was higher in the 5-month old callus culture, but the ploidy level was the same. In the callus lines derived from autotetraploid plants, cells with reduced chromosome number appeared quite frequently along with diploid and polyploid cells.